The present invention relates to a display unit for a measuring instrument with a display screen that has dot-sized, individually controllable image elements, commonly referred to as pixels.
Display units of this kind are used in a great variety of measuring instruments which, in particular, includes balances. With the individually controllable pixels, it is possible to represent symbols such as alphabetical and numerical characters of almost any shape and size, as well as pictorial symbols, graphs, etc., in the most diverse and dynamically changing arrangements.
A primary application for the display unit is to represent values of measured quantities in real time. A correct and clearly legible representation is particularly essential in a case where the operator has to take some kind of action based on the value of the measured quantity, such as controlling a speed, setting the magnitude of a current, or weighing a prescribed quantity of a substance. It is possible to use a digital display format for the measured quantity, but it is difficult to follow the progress of the measurement from the constantly changing digits. Also known are displays with graphic pointer elements, such as arrows, lines or the like, that sweep along a graduated scale to indicate the measured or weighed quantity. The latter concept is generally more suitable to inform the operator at a glance about the status of the measurement.
An arrangement of graphic pointer elements of this kind for a coarse and fine indication, respectively, is shown in the European patent application EP-A 0 128 296, where each of the pointer elements moves in a circle, comparable to the hands of a clock. This kind of display can be realized without moving parts, e.g., by optically projecting the pointer elements onto an image screen. However, the optical projection can have the undesirable effect of generating heat, which could be detrimental to the accuracy of the measurement. On the other hand, if a display screen is used in which individually controllable pixels are arranged in two axial directions of a grid, the heat problem can be brought under control, but a line-shaped pointer element that sweeps in a circle like a clock hand has to be formed as a dynamically changing image through a varying sequence and combination of pixel dots. In a moving state, the image gives an irritatingly uneven and jumpy impression to the viewer, which can easily lead to operator fatigue.
It is therefore the object of the present invention, to control a measuring instrument display composed of pixel dots in such a manner that an uneven and jumpy image is avoided.
The present invention offers a solution to the problem described above by providing a display unit for a measuring instrument, and more particularly for a balance, with an image screen that displays arbitrary symbols composed of individual image dots, i.e., a so-called dot-matrix screen. The image screen has an array of pixel elements in the size of the image dots, which are individually controllable by means of a control device and are aligned in the directions of the grid axes of the dot matrix. The control device (consisting of an arithmetic unit, a memory unit, and a display driver unit) controls a pointer element designed to give the appearance of moving within a display field. The inventive display unit is distinguished in that the pointer element maintains a constant slope angle (xcex2) as it sweeps over the display field. The basic concept of the invention is to use only pointer elements that maintain an invariant slope angle in relation to an axis of the pixel grid. The apparent sweep effect is created through a translatory movement in which the pointer element remains parallel to itself.
In one of the preferred embodiments of the invention, the pointer element consists of two segments. A first segment extends in the direction of one of the grid axes. The segments are composed of individual bar elements that are aligned parallel to the other grid axis. The bar elements are staggered at a different pitch in the first segment compared to the second segment, so that the two segments meet at a corner or break point. The position of the pointer element is varied by moving the break point along the direction of the first segment and adjusting the length of the latter, while at the same time moving the second segment parallel to itself in the direction in which the bar elements are aligned and adjusting the length of the second segment.
In another preferred embodiment of the invention, the pointer element is constituted of two different lines or rows composed of image dots. A first row of image dots is oriented in the direction of one of the grid axes and movable in the direction of the other grid axis, while a second row of image dots is oriented in the direction of the latter (xe2x80x9cotherxe2x80x9d) axis and movable in the direction of the former grid axis.
In many measurement processes, the end result has to match a prescribed target value. In this case, it is advantageous if the display not only indicates the momentary result of the measurement, but also the amount remaining to reach the target, where the remaining amount is shown with a higher degree of sensitivity, if possible, i.e., in a so-called fine-indication display. The problem to be solved by the invention occurs specifically in the display indication of a balance on which a material sample of a prescribed weight is to be prepared. Up to a point closely before the target weight, the material can be dispensed onto the balance relatively quickly (and the weight indication in this phase can be relatively coarse), but the last remaining amount has to be added very carefully while closely observing the progress of a sharply defined indication. In principle, the problems are analogous for every control process in which a measured quantity has to be matched to a target. A coarse and fine display for this kind of process can also be realized with the display unit according to the invention by using an arrangement where the coarse indication is represented by a part of the pointer element that moves in one axial direction of the pixel grid, while the fine indication is represented by a part of the pointer element that moves in the other axial direction of the pixel grid.
Preferably, in the coarse-/fine-indicating display according to the invention, the first and second grid axes of the dot matrix are substantially perpendicular to each other. In particular, the grid axes are oriented in the transverse or horizontal direction and in the up/down or vertical direction of the display field.
In the aforementioned embodiment where the pointer element has two segments connected at a break point, it is preferred if the sweep of the second segment of pointer element serves to provide the fine weight indication. The coarse indication is realized by setting the break point at a stationary position corresponding to a minimal length of the first segment and by activating a weight-dependent portion of the bar elements of the second segment.
As an alternative to the foregoing concept, the coarse indication may be realized (with the break point set again at a stationary position corresponding to a minimal length of the first segment) by successively activating a weight-dependent number of bars that are arranged above one another, each of them filling the space between one of the bar elements of the second segment of the pointer and the nearest border of the display field.
Expanding further on the same concept, during the phase of coarse weight indication, a mirror-symmetric stack of bars could be successively activated on the other side of the display field adjacent to the opposite border.